Fig. 4. Histograms of the proportion of steps that contained one through seven action potentials. (A) The distributions are statistically indistinguishable between flat (black) and rough (blue) terrain running, indicating that this parameter (spike number) was not modified by typical rough terrain perturbations. Neural modulation of spike number was evident during the large ascending perturbation at the start of the rough terrain (B) and during the final large descending step (C).